1. Field of the Invention
The present invention relates to an image forming apparatus such as electrostatic copying apparatus, electrostatic printer, or the like having cleaning means for cleaning an image carrier by scraping the image carrier by magnetic particles held by means for holding the magnetic particles.
3. Related Background Art
Hitherto, there has been well known an image forming apparatus in which a sheet-shaped transfer material such as a paper of the like is brought into with a transferable toner image formed on the surface of an image carrier, this toner image is electrostatically transferred to the transfer material, the transfer material is then separated from the image bearing member, the residual toner which does not contribute to the transfer and remains on the surface of the image bearing member is removed by proper cleaning means such as a cleaning blade or the like, and these processes are repeated. In such an image forming apparatus, in recent years, miniaturization and weight reduction are being accomplished more and more. Further, ease in maintenance and simplicity of operation are demanded. In consideration of these points, as an image bearing member, an amorphous silicon photosensitive material is preferably used because the Vickers hardness is so high as to be about 1000, the durability is high, and the potential stability is good.
However, even in the case of an amorphous silicon photosensitive material, when it is repetitively used, it becomes sensitive to humidity and water is easily absorbed into this material, so that an image defect such as image flow or the like occurs. Particularly, when the apparatus is set to the inoperative mode for a long time, a degree of the trace flow of an electrifier which is caused in the surface portion of the photosensitive material which faces the transfer and separating electrifiers and an electrifier for generating an AC corona is large, causing a problem.
Several causes of such a state are considered. First, it is considered that the corona product which is produced due to a high voltage generating member existing in such a kind of apparatus is deposited onto the surface of the photosensitive material and absorbs the moisture component, a resistance value of the deposited corona product becomes low, so that the charges adapted to form an electrostatic latent image leak in the lateral direction. Second, it is considered that for the trace flow of the electrifier, the volatile ozone product deposited onto a shielding plate of the electrifier moves to the surface of the photosensitive material when the apparatus stops.
Further, since many dangling bonds exist in the silicon atoms which construct the photosensitive material, they are sealed and linked by the hydrogen atoms. However, when the photosensitive material is repetitively used, the hydrogen atoms are disconnected, so that a more stable oxygen coupling occurs. When a concentration of the oxygen coupling increases, the electrostatic latent image forming charges leak in a manner similar to the above case because oxygen is hydrophilic. This point is also considered to be the third cause.
Even when considering any of these causes, in order to avoid the occurrence of such an unpreferable situation, hitherto, there has been proposed a method whereby the image carrier is heated by proper heating means to thereby eliminate water, a method whereby the surface of the photosensitive material is scraped by a cleaning roller consisting of an elastic material like a rubber or the like to thereby eliminate the ozone product, or a method whereby the surface layer which becomes sensitive to humidity is ground and removed.
However, since the amorphous silicon photosensitive material has such a characteristic that the charging capability deteriorates due to the heating, it is unpreferable to use the heating means. On the other hand, according to the method of grinding the surface of the photosensitive material by the cleaning roller, a grinding variation occurs, so that there is a fear such that such a grinding variation causes a sensitivity variation of the photosensitive material and, further, a deterioration of the image.
Further, there have been proposed a method whereby a magnet roller is used and the photosensitive material is scraped by using a toner brush formed on the magnet roller as is disclosed in Patent Application Laid-open No. 56-138774, and a method whereby a sleeve having therein a magnet roller is formed with a brush consisting of magnetic particles, the photosensitive material such as amorphous silicon or the like is scraped by this brush, and thereby preventing that the photosensitive material is excessively ground as disclosed in Patent Application Laid-open No. 59-121370. However, although even these methods are improved methods as compared with the foregoing method of scraping the photosensitive material by an elastic roller, the grinding of the photosensitive material still causes a problem.
On the other hand, particularly, in the case of using a color toner such as red, blue, or the like other than black, which has been used in the recent image forming apparatus, since the color toner is generally a nonmagnetic material, it is difficult to collect it by the magnet roller or the like and a toner brush cannot be formed.